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  • Ambiguous question on Reserved Instances

  • endian

    May 29, 2022 at 8:09 am

    “57. Question

    Category: CSAP – Cost Control

    A pharmaceutical company has a hybrid cloud architecture in AWS. It has three different accounts for its environments: DEV, UAT, and PROD, which are all part of the consolidated billing account. The PROD account has purchased 10 r4.16xlarge Reserved EC2 Instances in the us-west-2a Availability Zone. Currently, there is no running EC2 instance in the PROD account because the application is not live yet but in the DEV account, there are 5 r4.16xlarge EC2 instances running in the us-west-2a Availability Zone. In the UAT account, there are also 5 r4.16xlarge EC2 instances running in the us-west-1a Availability Zone.

    In this scenario, which account benefits the most out of the Reserved Instance pricing?”

    The answer depends on whether the RIs are zonal or regional. For regional, the answer will be ‘both the DEV and UAT accounts’. For zonal, the answer will be ‘only the DEV account’.


    A Reserved Instance that is purchased for a Region is called a regional Reserved Instance, and provides Availability Zone and instance size flexibility.

    – The Reserved Instance discount applies to instance usage in any Availability Zone in that Region.

  • Kenneth-Samonte-Tutorials-Dojo

    June 5, 2022 at 12:51 am

    Hi Endian,

    Thank you for your feedback on this question.

    The question state that the purchased Reserved EC2 instances are on us-west-2a. Therefore, We can assume that this is Zonal reserved instances.

  • Kenneth-Samonte-Tutorials-Dojo

    June 5, 2022 at 12:57 am

    For Regional Reserved instances, you don’t specify the Zone of the instances when you buy the Reserved Instance.

    Zonal Reserved instances only show up when you enable the “Only show offering that reserve capacity” when you search for Reserve Instances to buy.

    Zonal Reserved instances guarantees that a capacity is reserved to you on that zone and is available whenever you need. Regional Reserved instances does not guarantee the instances for that capacity reservation.


    Hope this helps.

    Let us know if you need further assistance. The Tutorials Dojo team is dedicated to helping you pass your AWS exam!


    Kenneth Samonte @ Tutorials Dojo

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